Mrs. Romney added, after an especially loud burst of cheers from the audience in Boston, “He was on the radio all the time for us in Ohio.”

All told, Trump participated in more than a dozen radio interviews and robo-calls statewide in Ohio. And ABC News has learned that many more American voters will soon be getting a call from “The Donald” too.

“Voters across the United States should expect a call from Donald Trump praising Mitt Romney for his tough stances on China, OPEC and other foreign countries that are depriving Americans of opportunities and jobs so that they can fulfill the American dream,” confirms Trump Executive Vice President & Special Counsel Michael Cohen.

Trump has been working on a national robo-call -- a type of automated message -- for the Romney campaign, taking his efforts for Romney from focused states with upcoming contests to an all-50-states approach. “Conversations continue with the Romney campaign managers seeking Mr. Trump’s continued assistance in states to ensure additional Romney victories,” said Cohen.

Ohio is the most recent example of Trump’s primary season handiwork. The business mogul did similar stumping last week in Michigan and is participating in fundraising for Romney as well.

Cohen points to Romney’s strong surrogate network as a way for the candidate to get around his trouble connecting with voters.

“Supporters like Mr. Trump introduce voters to the real Mitt Romney. And once that happens, people believe in him, believe in his campaign and go out to vote for him in the primaries and caucuses,” he said.